1. Field of Use
The present invention relates to a method and apparatus for obtaining measurements of induced resistivity of objects from confined spaces such as within the confined space of a down-hole hydrocarbon production well. It is well known that measuring the resistivity of an object or media can provide useful information regarding the composition and the location of object or media. The present invention utilizes the principles of Magnetic Antenna(trademark) and Magnetic Lensing(trademark) to obtain information regarding the location and properties of the target object.
2. Description of Related Art
In many applications of Inductive Resistivity Measurements (IRM), limitations of space or topography prevent the use of multiple antennas arrays. This lack of multiple antennas arrays causes the loss of directional information from received EM waves. An example of space limitations is in the down-hole environment of oil wells. IRM is used in this application for reservoir mapping or the detection of interfaces among oil, water and gas in a geologic formation. The accurate knowledge of the direction of the reflected EM wave is very important in these uses of IRM. Directionality determination must be made in both the vertical and azmuthal senses. Therefore there is a need for a device to encode the radiated EM signals in a way that yields directionality in space limited environments.
One requirement when obtaining useful or reliable Inductive Resistivity Measurements (IRM) is the ability to determinate the direction, if not the location, of the target object in which resistivity has been induced and now subject to measurement. This directionality makes it possible to determine the location of various objects in which the resistivity has been induced. A customary method of locating the source, or at least ascertaining the direction of the induced signal, is to utilize multiple antennas or signal receiving devises. Measuring the signal from multiple locations provides multiple references points for determining the location based upon conventional coordinate systems or other known methods. Determining the location or the direction of an object in which resistivity signals are induced has provided significant challenges. Prior to the present invention, the utility of IRM in such applications has been severely limited.
The present invention utilizes Magnetic Antenna and Magnetic Lensing techniques to overcome the spatial limitations that heretofore have prevented multiple measurement to be taken from separate locations. Simply stated, the method and apparatus of the present invention discloses creating phase changes in a pulsed or oscillating magnetic flux transmitted from a magnetic flux transmitter. The phase changes are created in a controlled manner by utilization of the Magnetic Lensing effect. As the transmitted oscillating magnetic flux passes through differing sections of a Magnetic Antenna, the phase of the original oscillating flux is modified into multiple phases. These multiple phases are also oriented in different directions. Accordingly, a flux from a single source and having a single phase, is altered into multiple and easily distinguishable flux signals. Further, since the multiple flux signals can be oriented in different directions by the Magnetic Lens effect, it is possible to utilize the different induced phases from one or more magnetic flux transmitter to induce responsive oscillating flux signals within the target object from one or more of known locations relative to one or more signal receiving devices. These results in multiple Induced Resistivity Measurements that can provide the location or, at a minimum, the direction of the target object from the separate signal receiving devise.
Accordingly, it is an object of the present invention to provide a method and apparatus for creating multiple and distinguishable signals from a single source and utilizing at least one such signal for locating objects having electrical conductive properties.
It is another object of the present invention to utilize one or more receiving devices to determine the location, as well as direction, of one more electrically conductive objects within a geologic formation or other media surrounding the invention.